The Behavioral Science Core (BSC) provides behavioral scientists with facilifies, tools, and expertise to enable them to capture and characterize variations in human behavior in normal and atypical human development. CHDD behavioral and biobehavioral scientists are involved in collaborative research with scientists from a wide range of other disciplines. Many focus on behavioral and developmental patterns as part of multidisciplinary studies. Others focus on specific ecological influences and intervenfions affecfing proximal interactions involving dyadic and group relationships of adults and children in naturalistic and laboratory setfings. All of these studies require careful characterization of behavioral variation, outcomes, and phenotypes. Such characterization is becoming increasingly complex, requiring methodologies which can capture behavior with precision at multiple levels of analysis. Core facilities in the BSC include state-of-the-art behavioral recording systems that capture the subtle timing and confingencies of behavior and social interacfion that cannot be captured in other ways and which facilitate reliability in testing and coding for a variety of neurocognitive and related domains. The data captured with these video recording systems are then being linked with sophisticated coding systems and stafisfical packages to enable investigators to efficienfiy code the data at both molar and molecular levels that are effortlessly and accurately synchronized with a digital time stamp. Consultation is also available regarding conceptual issues pertaining to measurement and analysis of specific constructs (e.g., parent-child interaction, peer relations, attachment).